Why Does the Shoulder Click or Pop?

Understanding Shoulder Sounds

Clicking, popping, grinding, clunking, and crackling sounds in and around the shoulder are among the most frequently reported concerns by patients — and among the most commonly misunderstood. For many people, these sounds generate significant anxiety: does the click mean something is tearing? Is the popping damaging the joint? Should I stop using my shoulder until it is investigated? In the majority of cases, shoulder sounds are benign mechanical phenomena that carry no pathological significance — but in certain contexts, they represent genuine structural pathology that warrants clinical assessment and management.

The key clinical question is not simply whether the shoulder clicks, but whether it clicks in conjunction with pain, catching, instability, or loss of function. Pain-free sounds are almost universally benign. Sounds accompanied by pain, mechanical symptoms, or functional limitation deserve investigation.

Joint Cavitation

The familiar cracking sound produced by deliberately popping a knuckle — or that occurs spontaneously during shoulder movement — is produced by joint cavitation: the rapid formation and collapse of gas bubbles within the synovial fluid of the joint. When a joint is distracted or rapidly moved, the intra-articular pressure decreases below the cavitation threshold of the dissolved gases (primarily carbon dioxide) in synovial fluid. Gas bubbles form and then collapse rapidly, generating a single audible crack. The joint cannot be cracked again until the gas has been reabsorbed into solution — typically requiring fifteen to thirty minutes.

Cavitation is entirely benign. Multiple high-quality studies have found no association between habitual joint cracking and arthritis, cartilage damage, or joint disease. The crack itself is a pressure event, not a tissue event.

Tendon Snapping and Subluxation

A more clinically informative clicking mechanism involves tendons snapping over bony prominences or subluxing — temporarily displacing — from their normal anatomical groove. The long head of biceps tendon, which runs through the bicipital groove on the anterior humerus, can produce a palpable and audible snap during certain shoulder movements if the transverse humeral ligament that retains it is lax, or if the groove morphology is abnormal. This tendon subluxation is typically accompanied by a sharp, anterior shoulder pain and a catching sensation. Subscapularis tearing can also allow medial subluxation of the biceps tendon, producing a reproducible click with internal and external rotation.

Snapping of the posterior shoulder tendons, including the infraspinatus and teres minor, over the posterior glenoid rim produces a different quality of sensation — typically a dull thud or clunk felt posteriorly, often associated with the posterior capsular tightness common in throwing athletes.

Labral Pathology

The glenoid labrum is a fibrocartilaginous rim that deepens the shallow glenoid socket and provides the attachment point for the glenohumeral ligaments. Labral tears — including the SLAP (Superior Labrum Anterior to Posterior) tear common in overhead athletes and the Bankart lesion associated with anterior shoulder dislocation — can produce a characteristic mechanical clicking, catching, or clunking sensation during shoulder movement. The torn tissue intermittently catches between the articular surfaces of the glenohumeral joint during rotation, producing both the sound and a sharp, catching quality of pain that patients typically describe as distinct from the background aching of rotator cuff pathology.

Labral clicking is frequently position-dependent and reproduced during specific provocative tests including O'Brien's active compression test and the crank test. Distinguishing labral from other sources of clicking requires clinical testing and, where indicated, MRI arthrography.

Scapular Dyskinesis and Crepitus

The scapulothoracic articulation — the interface between the scapula and the posterior thoracic cage — can generate crepitus (grinding or grinding sounds) when abnormal scapular motion brings bony prominences into contact with the ribs. Scapular dyskinesis — altered scapular kinematics driven by periscapular muscle weakness or inhibition — is the most common cause. When the serratus anterior and lower trapezius fail to provide adequate dynamic scapular control, the scapula may winging (medial border lifting from the thoracic cage) or tilting (inferior angle anteriorly displaced), bringing the superomedial corner of the scapula into contact with the underlying ribs during arm elevation. The resulting grinding is felt and heard at the scapular angle and is typically painless or only mildly uncomfortable — though the underlying dyskinesis may be contributing significantly to shoulder impingement symptoms through its effect on subacromial space dynamics.

Degenerative Crepitus

In the context of glenohumeral or acromioclavicular joint arthrosis, persistent crepitus — a rougher, more continuous grinding sensation and sound throughout movement — reflects the articulation of irregular, degraded cartilage surfaces. Unlike the single-event crack of cavitation, degenerative crepitus is continuous, present throughout the arc of movement, and typically associated with stiffness, reduced range of motion, and activity-related pain. It is a feature of established joint degeneration rather than a cause of it, and its presence indicates the need for a management approach that addresses load distribution, joint mobility, and surrounding muscle function.

When Is Investigation Warranted?

Pain-free clicking — regardless of its frequency or loudness — generally does not require investigation. Investigation is warranted when clicking is accompanied by pain; when a catching sensation suggests mechanical interference within the joint; when there is accompanying instability, weakness, or loss of range of motion; or when the history includes significant trauma, overhead sport demands, or a prior dislocation. Ultrasound is the initial preferred imaging modality for tendon assessment; MRI arthrography provides superior labral evaluation. Clinical assessment by a practitioner experienced in shoulder evaluation typically provides sufficient information to guide appropriate triage without requiring immediate imaging for all presentations.